How to color in region based on postal code using Leaflet?

Question

I'm trying to color in an entire region on my map based on a Postal Code. So I want the entire postal code region to be colored in basically. I am using the plugin Leaflet for this.

Right now I display circles on the map (Click the link to see): Current Map

This is the JS code I am using to display it:

   $(document).ready(function(){
        /* Initialising the map */
        var map = L.map('map').setView([50.84673, 4.35247], 9);

        L.tileLayer('https://tile.openstreetmap.be/osmbe/{z}/{x}/{y}.png', {
            attribution:
            '&copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors' +
            ', Tiles courtesy of <a href="https://geo6.be/">GEO-6</a>',
            maxZoom: 18
        }).addTo(map);

        var popup = L.popup();

        function onMapClick(e) {
            popup
                .setLatLng(e.latlng)
                .setContent("You clicked the map at " + e.latlng.toString())
                .openOn(map);
        }

        map.on('click', onMapClick);

        // Fetching the postal codes for each representative
        $.ajax({
            url: dynamicmapurl,
            method: "GET",
            dataType: 'json',
            beforeSend: function(xhr, settings) {
                if(!csrfSafeMethod(settings.type) && !this.crossDomain) {
                    xhr.setRequestHeader("X-CSRFToken", csrftoken);
                }
            },
            success:function(data)
            {
                data = data.reverse();

                for(var i = 0; i < data.length; i++){

                    //Drawing a circle on the map based on the
                    //Postal code dictionary array I'm receiving from the backend
                    L.circle([data[i].lat, data[i].lon], 500, {
                        color: data[i].fillColor,
                        fillColor: data[i].fillColor,
                        fillOpacity: 0.8
                    }).addTo(map).bindPopup("Vertegenwoordiger: " + data[i].vertegenwoordiger + " <br> " 
                        + " Postcode: " + data[i].postcode)
                }
            },
            error: function(data){
                console.log(data);
                alert("Algemene Error");
            }
        });
    })

Is there a way to color in the entire postal code range on the map using the Leaflet plugin? If so, how would I go about this?

Result I want: Click on link to see

Note: the region should be colored in depending on which representative & the map should not be so dark.